Method and apparatus for the surface treatment of metals



Feb. 6, 1951 w, THOMAS ET AL 2,540,602

METHOD AND APPARATUS FOR THE SURFACE TREATMENT OF METALS Filed July 5, 1946 I 2 Sheets-Sheet 1 INVEN'TORS FRANK W. THOMAS BY Eu Smou 2 x Agent Feb. 6, 1951 w, THOMAS ET AL Y 2,540,602

METHOD AND APPARATUS FOR THE SURFACE TREATMENT OF METALS Filed July 3, 1946 2 Sheets-Sheet 2 'IIIIIIII/IIIIIIIIII[III/IIIIIIIIIIIIIIIIII/lll/I/I/llI/I 66 67 p 68 as E I INVENTORS FRANK W. THOMAS 1:: BY Eu SIMON Patented 6 -METHOD AND APPARATUS FOR SUR- FACE TREATMENT OF METALS Frank W. Thomas, 'Burbank, and Eli Simon, Los Angeles, Calif., assignors to Lockheed Aircraft Corporation, Burbank, Calif.

Application July}, 1946, Serial'No. 681,224

This invention has to do with the surface treatment of metals, and has more particular reference to the anodizing of parts, components, sheets, etc., of aluminum, aluminum'alloys, magnesium, magnesium alloys, and other metals. It is the widespread practice in the aircraft industry, and other industries, to provide or deposit anodic coatings on aluminum and magnesium alloy parts and assemblies to obtain corrosion resistant surfaces and to preparethe surfaces for the increased adhesion of primers, paints and adhesives. The usual procedure is to totally immerse "the parts in an appropriate electrolyte and to connect the parts in an electrical circuit so that they form the anode. In the case of large components and assemblies it is necessary to maintain large tanks of electrolyte for their total immersion, and it becomes impractical to anodize eittremely large assemblies or to repair the surfaces of previously anodized parts that have become scratched or abraded. Furthermore, the conventional anodizing'process is extremely timeconsuming, and 'an anodizing period of about one-half an hour at a current density of one ampere per square foot is usually required'with achromic acid electrolyte to obtain a good corrosionresistant surface on aluminum alloy parts. The prolonged immersion is necessitatedbecause itis impractical to obtain any substantial current density when employing the immersion system. There are many cases where the processing and assembling sequence does notv permit the use of the tank or immersion or anodizing procedure. It is an object of the present invention to provide a method for the anodizing of aluminum.

for'the production of an effective :anodic coating is. markedly reduced. In addition, it is unnecessary to handle the parts in order to introduce them into a'tank or to remove from a bath at the completion of the operation.

'--.Another object of the invention is to provide an; anodizing method that is flexible and capable of employment in many situations where'theimmersion process is useless, or at least impractical.

7 Claims. (Cl. 204 15) The present method 'is useful in repairing scratched or abraded anodic films previously-ap plied, in touching up assemblies of a'n'o'dicparts, in anodizingdefined or given portions'of assem blies, assemblies having bi-metal parts or noncompatible compounds which cannot be im-"- mersed in an'electrolyte, and in anodizing one or both-surface areas of sheets, etc. The'method may be successfully employedto obtain g00d-;corrosion resistant films'on any surface areas'that can be reached with a manually manipulated brush or pad, or'bya power driven roller.

Another object of the invention-is to provide a method ofthe character referred to that re quires a minimum-amount of equipment. The apparatus required may be portable, light in weight, and inexpensive to-install andmaintain;

Another object of theinvention isto provide a simple, practical andinexpensive apparatus for producing or depositing anodic' films on 'parts and assemblies of aluminum, aluminum 'alloys, magnesium,magnesiumalloys, etc. In one embodi-f merit of the invention theequipment consists of' a simple-brushcontaininga supply ofelectrolyte plying means embodied therein or associated.

therewith so that "electrolyte may be supplied to; The brush may be con-,' Veniently manipulated "by a single workman and employed in'a manner simil'ar to a conventional paintbrush. The-fact that A. C. power maybe" employed, makes it possible to plug in" the brush wherever the usual'11'0volt AC. power is avail-' able. In another form,'the'apparatus comprises; a pad adapted to be applied to the part to be" anodized and saturated with a selected electrolytel This-form of the apparatus provides for the rapid. formation of an anodiccoating on a substantial; surface area, either flat or "curved. In still an-'-1 other application ofth-e' invention the apparatus comprises a pair of rollers,eith-er one orboth of: which-carries a pad saturated with a selected 1 electrolyte-'to treat'the surface or surfaces of a" the brush head at'will.

sheet, or the like, tube run between the rollers.

Another object ofthe invention'is to'provi'de' apparatus-or equipmentfor the anodic coating with a source of electrical energy.

.Aiurther. object of the invention is to provi'de apparatus of the kind referredtothat isoperable 'brush or applicator.

tion and the electrical circuit in a diagrammatic manner;

Figure 2 is a perspective view illustrating another form of the invention in position on a part being treated;

Figure 3 is a more or less diagrammatic perspective view of still another form of the apparatus with the electrical circuit shown in a diagrammatic manner; and

Figure 4 is a view similar to Figure 1 showing still another embodiment of the invention, the piping system being shown in a diagrammatic manner.

It is believed that the method or process of the invention will be best understood following adescription of the apparatus. Accordingly, we will first proceed with a detailed description of several preferred forms of the apparatus and will then set forth the method as employed in operating the apparatus, it being understood that the invention is not to be construed as limited to the specific details herein described.

In Figure 1 we have shown a form of the invention embodying a manually manipulatable The brush comprises an Outer shell or tube II] of a dielectric material that has the required strength and rigidity, and that is resistant to the hot electrolyte. In practice the tube Ill may be formed of Micarta. Th tube I is proportioned so that it may be readily grasped and held in one hand, and while we have shown a simple cylindrical tube, it is apparent that the member may be externally contoured to more readily fit the hand. The outer end of the tube I0 is Open, while its inner end contains the brush II to be described below. A liner I2 of metal is secured in the tube III. The liner is constructed of Dural (a wrought aluminum alloy containing from 3.0 to 4.5% copper, from .4 to 1.0% magnesium, from 0.0 to 0.7% manganese, and the balance aluminum), or like material, that is resistant to the electrolyte and that forms a good electrical conductor. The outer end of the liner I2 may be flush with the end of the tube III, but the inner end of the liner is spaced some distance from the inner end of the tube so that the liner cannot contact or come in close prox-- imity to the part P being treated or worked upon.

The above mentioned brush II is engaged or secured in the inner end. of the liner I2, and extends beyond the tube I0 so that it may be moved across the surface of the part being anodized. The invention contemplates the employment of a pad or brush I I constructed of any selected material that is capable of carrying or becoming saturated with the electrolyte. For example, cotton fiber, porous rubber or sponge rubber may be employed. We prefer to use a pad of glass wool. The shank portion of the pad is tightly wound with wire I3 to be cylindrical in form, and to tightly engage in the sleeve I2. The pad or brush extends outwardly through the tube I0 and flares to have a free exposed active portion overlying the ends of the tube II). It will be observed that the pad or brush II may be easily replaced when worn.

The apparatus of Figure 1 further includes means for drawing or pumping liquid electrolyte into the liner I2 and for forcing the electrolyte out through or into the brush II. This means also serves to conduct electricity to the sleeve I2 for delivery to the electrolyte in the pad II. A piston I4 i removably arranged in the liner I2 and is preferably equipped with a series of circumferentially spaced spring-urged balls I 5 for riding on the surface of the sleeve to assure an uninterrupted electrical engagement between the piston and sleeve. The balls I5 and their springs are contained in radial sockets in the piston I4, which is metal and a good electrical conductor. An O-ring I6 of synthetic rubber, or similar ma terial, is contained in an annular groove in the piston I4 to maintain a sliding seal between the piston and liner. A piston rod I! is secured to the piston I4 and extends rearwardly through the liner I2 to normally extend beyond the tubular applicator.

The interior of the linear I2 constitutes a res ervoir for containing a sufiicient suppl of the electrolyte to maintain the pad or brush II in a saturated condition for the treatment or anodizing of a considerable surface area of the part or parts to be treated. To fill the reservoir, the pad or brush end of the applicator is immersed in the body of the electrolyte and the piston I4 is moved outwardly so that the electrolyte is drawn into the reservoir. As the applicator is used, the rod I1 is moved inwardly from time to time to force electrolyte into the brush I I in order to keep the same fully saturated. I

The electrical supply system for the applicator of Figure 1 comprises a generator I8, or other suitable source of electrical energy, a lead I9 extending from the generator to the piston rod I'I and a second lead 20 from the generator extending to the part P to be anodized. We have shown a terminal 2| securing the wire I9 to the rod and a releasable clamp 22 on the wire 20 for clamping onto the part P. The circuit arrangement is such that the liner I2 forms the cathode and the part P, the anode. A potentiometer 23 is interposed in the line 20 so that the current density at the point of the anodizing operation may be varied at will. We have also shown an ammeter 24 connected in the lead l9 and a voltmeter 25 connected in a line bridging the generator or power source. While we have shown a generator I8, it is to be understood that any suitable source of D. C. current may be used, and that the lines I9 and 20 may be simply pluggedinto a source of alternating current, such as a conventional volt supply.

In carrying out the process of the invention with the apparatus of Figure 1, the part P, or at least the surface thereof, t be anodized, is thoroughly cleansed of foreign matter. The applicator is supplied with a quantity of the electrolyte as described above, and the wires IE} and 20 are connected with the piston rod I! and the part P. With the potentiometer 23 adjusted to the selected setting, the operator simply wipes the pad II back and forth across the surface of the part. The'thickness of the anodic film formed in this manner is a function of the speed and number of brush strokes, the particular electrolyte solution employed, the current intensity and other factors such as the temperature. The potentiometer I8 may be adjusted to obtain any selected current density at the saturated brush I I.

- II of limited area provides for a highly concen- In' this connection it will be observed that the brush" trat'd action, there being a high current-density attheelectrolyte in the brushit'o obtainthe rapid formation of an anodic film on the part P. -In practice, the current density-at the surface of the part P and brush I1 is many times greater than that obtainable with the immersion anodizing method. The voltage and current applied depend upon the electrolyte employed and where the brush is about one inch in diameter we may use 7 from '20 to 200 volts, and from one to fifteen am peres, in accordance with the character of the electrolyte, it being understood that any desired or selected current strength may be used. In a typical preferred case the wires 19 and '20 are connected with the opposite sides of an electri'cal energy source supplying a voltage of from 20 to '200 volts "and a, current density of from approximately 180 to approximately 2,750 amperes -per square foot. I The electrolyte supply to the brush ll may be a saturated solution of 130*- tassium acid sulphate, an aqueous 'chromic anhydride-solution, or any other suitable electro- The number of brush strokes required will depend upon the nature of the part P, the current 'strength, the electrolyte "employed, etc, but

in most instances where a D. C. current at approxin'r'atel y 500 amperes per square foot is used, we have found that from fifteen to twenty-five brush strokes will produce a good a'no'dic film.

Satisfactory coatings or films are obtained when the electrolyte is a three per cent aqueous solutionof chromic acid, and a normal A. C. current supply 'of about 110 volts is used. When the part to be treated is magnesium or a magnesium alloy, the'electrolyte preferably comprises a mixture of tungstate or 'van'adate salts and chromic acid adjusted to a pH of seven. The applicator may lii-pulatablernay be kept insubstantian COnti'nu ou'sservice by the'operator. w

"In Figure 2 we have illustrated another'appl-ication of the invention. In this case, a mat or pad '20 of fiber-glass Wool, or cellulose material is provided and a metal screen or shetZ'l "is engag'e'dover the pad. The pad 20 is adapted to be arranged on the surface to be treated. We have shown the "pad 20 engaged overthe surface of the leading edge section 22 "of the airplane wing, it being understood that the pad may be formed for application to other parts. The pad may be 'sufiiciently large to cover a substantial area, and'is flexible or pliable so as to conform to the contour of the part. .The sheet 21 may be considered the cathode and is a 'metal element in the nature of a wire screen, perforated foil sheet, or a perforated sheet metal member. In the particular case illustrated, the sheet 2| is a perforated plate or'sheet metal'part. The cathodesihet 2| maybe flexible to conform to the pad 20, or may be substantially rigid and shaped to follow the general contour of the part to be treated. 4

I In using the apparatus of Figure 2, the surface or the part 22' is first cleansed and is then crushed with the electrolyte. The mat or pad 20 is either saturated with "the "electrolyte and mesapia'ceatnuie surface, or is-first arranged 6 in filace: 6n the shriaeeand then saturatedwith the electrolyte; 'Tn'e shield or cathode sheet 21' i'splaice'd o'vef tl'l'e-padih and made to conform thereto. It is desirable to retain the-pad 20 in close engagement with thepart 22 and this may be accomplished. by arranging adhesive tape 23' over. the sheet and onto the part 22' as show-n or if desired, wire, straps, or the like, may be employed for this purpose; The above described Wire [9 is then secured to. the cathode sheet 21: by a. clamp M, and the wire 20 is attached to the part 22' by a similar "clamp 25'. The a'sse'nr--- bly is now ready for the anodizing operation. Upon applying current to the circuit IQ-=20, the anodic coating or film is formed on the surface of the part 22'. An efiectivecoating. provided by applying-approximately -20 amperes per square foot of surface being treated at from 10 to 20 volts, using; a potassium bisulfate electrolyte, and for a periodof from two to ten minutes. It isdeisirable. to supply additional electrolyte ,to the pad 2l l;f-rom time to time to. prevent the development of local dry spots at thesurface of the part 22' Whenth'e pad 20 is formed of fiberglass wool, or the like, the abovementioned electrolytes may be used, but where the :pad is of cellulose material a saturated solution of sodium or :potassium 'bisulfate is preferably used because ithas no marked degenerative effect upon the cellu-i'. lose. At the end of the selected treatment pe= riod,, the electrical circuit is opened. and the pad assembly is removed from the part 22. The surface of the section or part is then flushed or Washed with water.

Figure 3 illustrates a form of the invention suitable for thesurface treatment of sheets, elonate strips, etc. Thisdevfic comprises a suitablle fr arne tfl and a pair of rolls -'3l and 32. The rollsar v horizontally disposed one above the other and have. shafts 33' and which are carried in suitable bearings 35 on the frame. Either one orv both of the rolls. 3'] and 32 ;may form the cathode for the anodizing operation, and are formed of a suitable metal which is resistant to the electrolytes which may be used. Peripheral pads-36 of absorbent or porous material such as s onge: rubber or synthetic sponge rubber are provided on the rolls, and the rolls arerelated so that a sheets or similar part may be fed between them to be contacted. by the pads. It is preferable to drive or rotate the rolls so that the -part or sheet being treated may be po'sitively advanced or fed through the ions. We have s own a belt and pulley drive for the rolls 3'1 and 32, it being apparent that other forms of drives may be used. 'Ijh'e particular drive illustrated includes a belt 3"! extending f'rdr n a power source, not shown, 'al'ifi operating over a pulley on the shaft 33 or theroll] 31., and a crossed belt 38 dictating over pulleys. dnthe two roushafts so that both rolls are -s iv mujitan'edusiy-iotareu.

The apparatus or Figl ire 3 further includes mean for delivering electrolyte to the sheaths o'i'paas as of 'th'e'roll's-Sl and 32. This means s preferably such that electrol te may be supplied to either one '01 both of the T011 1121615. In tfi case illustrated, the electrolyte supplying means includes span or sum'p 39 arranged in the frame 30 belovvthe roll 'szin aposiiion where the 'pad sectoral; "roll 'inoves throughthe body of 'ele'c trolyte 40 contained inthe. sump. Thus, as the roll' 32 rotat s, fits pad 36 "is continuously re plenished with the electrolyte. "The inventidn contemplates supplyingthe electrolyte. to pad 36 *Of the upper 1 011 3| ith l by ite'rlial means such as a spray directed onto the pad, or by an internal means. In the drawings the roll 3| is hollow, and its peripheral wall has a multiplicity of perforations 4| so that electrolyte may be supplied to the interior of the roll for internal delivery to the pad 36. One end portion of the roll shaft 33 has a passage 42 communicating with the interior of the roll and extending to a rotary or swivel coupling 43 on the end of the shaft. A pipe 44 extends from the coupling 33 to the sump 45 or other source of electrolyte. A suitable pump 45 is interposed in the pipe 44 to deliver the electrolyte to the roll 3| and a valve 46 may also be connected in the pipe to control the delivery of the electrolyte.

' As mentioned above, the rolls 3| and 32 form the cathodes and spring contacts or brushes 41 are supported by an insulated bracket on the frame 35 to engage adjacent ends of the rolls. The electrical system or circuit of Figure 3 may be identical with that of Figure 1 and correspond ing reference numerals are applied to corresponding parts of the two illustrated circuits. The conductor I9 is connected with the brushes 4! and a clamp 48 may be employed to connect the Positive line with the part or sheet S.

In carrying out the method with the apparatus of Figure 3, the sump 45 is supplied with a suitable quantity of the electrolyte 40 and the leads l9 and 20 are connected with the brushes 4'! and the sheet S respectively. If it is desired to deposit an anodic coating on only one surface of the sheet S, the valve 46 is closed and the pump 45 is cut off. The sheet S is entered between the rolls 3| and 32 and the potentiometer 23 isadjusted to provide the desired current density at the surface of the sheet and the electrolyte carrying pad of roll 32. When the rolls are rotated, the sheet S is drawn between them and the pad 36 of roll 32 moves through the electrolyte to become saturated. The pad of the rotating roll carries the electrolyte into contact with the surface of the sheet S, there being current fiow from the cathode roll 32 through the electrolyte in the pad. The area of contact between the rotating pad 36 and the surface of the sheet S is rather limited so that the current density in the electrolyte at the surface of the sheet is concentrated, assuring a rapid anodic film-forming action. The sheet S may be passed between the rolls 3| and 32 several times to build up the anodic film to the desired thickness, the number of passes required depending upon the current strength, the character of the metal in the sheet S, the electrolyte, the temperature, etc. If desired, the speed of rotation of the rollers may be reduced to the extent that a sufficient film or coating may be deposited upon a single run of the part between the rolls. When both surfaces of the sheet S are to be treated, the procedure is: the same as just described except that the valve 46 is opened and the pump is operated so that electrolyte is supplied to the pad 35 of the roll 3 as well as to the pad of the roll 32. Following the coating or film forming operation, the surfaces of the sheet S are flushed or washed with water. In some instances it may be desirable to repeat the operations after such washing of the surfaces to build up a more effective anodic coat ing. The electrolyte employed with the apparatus of Figure 3 will be determined by the character of the sheet S or other parts being treated, and by the character of the pads 36 as, described above in connection with Figures 1 and 2. v

Figure 4 illustrates an applicator type of device associated with a remote source of supply of the electrolyte. The applicator includes a hole low or tubular handle 58 of any selected mate rial and a tubulr case 5| of Micarta or any other appropriate insulating material secured to the forward end of the handle by a releasable con nection 52. A block 53 of metal such as alumimum is secured in the handle and carries a rod 54 which extends rearwardly through the handle for connection with the above described wire l9. The forward end of the case 5| is open to receive the brush or pad. r

In this form of the invention the pad assembly is readily removable and replaceable so that the applicator may be equipped with pads of any required size. Th pad unit comprises a cup-like member 55 for retaining the root end of thepad 55 of fiberglass wool, cotton fiber, or other se-' lected material. A shank 51 is attached to the cup member 55 and extends rearwardly through a tubular sealing member 58 of rubber, or the like. The sealing member 58 is engaged in the case 5| and bears rearwardly against the block 5-3 while the cup member 55 seats rearwardly against the sealing member. The brush or .pad shank 5? has removable engagement or connection with the block 53. A tapering socket 59 is provided in the forward end of the block, and. the rear portion of the brush shank 51 is correspondingly shaped to nest or fit therein. It will be apparent how the brush or pad assembly may be removed and a replacement assembly of the required character and size may be installed.

The means for supplying electrolyte to the applicator is characterized by a remote source of the liquid. As diagrammatically illustrated, this comprises a tank 55 adapted to contain a sub.-: tantial supply of the electrolyte and a line or hose 5| extending from the tank to the applicator. Pump means or pressure applying means is provided to deliver the electrolyte to the applicator under pressure. In the arrangement illustrated, this comprises an air pressure line 62 discharging into the upper end of the tank and equipped with a release valve 63 and a pressure regulator 64, both of conventional construc tion. It is to be understood that other forms of pump means, such as a centrifugal pump in the line 6|, may be employed to force the electrolyte to the applicator. The line 6|, or at-least the portion of the line adjacent the applicator, is

flexible so as not to interfere with free manipue,

lation of the same. The line 6| connects with.;a fitting 55, which in turn communicates with an annular groove 55 in the shank 51. The groove 66 communicates by means of spaced radial ports with an axial passage 6! leading out through the shank and member 55 to the root'of. the pad 55. The fitting 65 is equipped with a valve 55 so that the operator may regulate the feed of the electrolyte to the pad. Y

The operation of the device shown in Figure 4 is the same as that illustrated in Figure 1, it being understoou that the electrical circuit |9-25 is connected with the rod 54 and the part P and is adjusted as above described. In this case the operator may regulate the delivery of electrolyte to the pad 56 as conditions of op;ration require, and there is no need to otherwise replenish the electrolyte.

While we have referred to the treatment of aluminum, aluminum alloys, magnesium and magnesium alloys, it is to be understood that the invention is not confined to such applications. For example, the method and apparatus may be 3 used in the treatment of foils of various metals and to treat parts of steel, brass, bronze, etc. Furthermore, in addition to providing corrosion resistant surfaces and surfaces for the application of paints, adhesives, etc., the method and apparatus are adapted to be employed to obtain decorative effects, increase the electrical resistance of foils, sheets, etc., and for other purposes.

Having described only typical forms of the invention, we do not wish to be limited to the specific details herein set forth, but wish to reserve to ourselves any variations or modifications that may appear to those skilled in the art and/or fall Within the scope of the following claims.

We claim: 7

1. The method of forming a corrosion resistant anodic coating on the surface of a metal part which comprises supplying a liquid electrolyte to a porous pad, connecting said part and pad with the opposite sides of an electric energy source which supplies a voltage of from 20 to 200 volts and a current density of from approximately 180 to approximately 2750 amperes per square foot, bringing the surface of said part and the pad into engagement, and moving the pad and part relative to one another while said engagement is maintained and while the part and'pad are connected with said energy source to progressively form a corrosion resistant anodic film on said surface.

2. The method of forming a corrosion resistant anodic coating on the surface of a metal part which comprises supplying a liquid electrolyte to a porous pad, connecting said part and pad with the opposite sides of an electric energy source which supplies a voltage of from 20 to 200 volts and acurrent density of from approximately 180 to approximately 2750 amperes per square foot, bringing the surface of said part and the pad into engagement, moving the electrolyte-containing pad across said surface while maintaining said engagement and while the part and pad are connected with said electrical energy source to progressively form a corrosion resistant anodic film on the surface.

3. The method of forming a corrosion resistant anodic coating on the surface of a part containing metal selected from the group consisting of aluminum and magnesium; said method comprising wetting a liquid-carrying member with an electrolyte, connecting said part and said member with the opposite sides of an electric energy source supplying a voltage of from 20 to 200 volts and a current density of from approximately 180 to approximately 2750 amperes per square foot, and moving the wet member across said surface while the part and member are con-, nected with said electrical energy source to progressively form a corrosion resistant anodic film on said surface.

4. The method of forming a corrosion resistant anodic coating on the surface of an aluminumcontaining part which comprises providing a manually manipulable absorbent pad, supplying an electrolyte to the pad, connecting said part and pad with the opposite poles of an electric energy source supplying a voltage of from 20 to 200 volts and a current density of from approxi-' mately 180 to approximately 2750 amperes per square foot, engaging the pad with said surface, and moving the pad across the surface while the part and pad remain connected with said electric energy source to progressively form the anodic coating throughout at least an area of said surface.

5. A device useful in forming anodic films on parts comprising a tubular dielectric member adapted to be grasped and manipulated by the operator, a metal liner in the member, a pad of absorbent material secured in the liner and extending from an end of the member so as to be engaged with the parts being treated, the liner being adapted to contain a supply of electrolyte for wetting the pad, and means for conducting electrical current to the liner and pad.

6..A device useful in forming anodic films on parts comprising a tubular dielectric member adapted to be grasped and manipulated by the operator, a metal liner in the member, a pad of absorbent material secured in the liner and extending from an end of the member so as to be engaged with the parts being treated, the liner being adapted to contain a supply of electrolyte for wetting the pad, a piston operable in the liner to draw electrolyte into the liner and to force electrolyte from the liner into the pad, and means for conducting electrical current to the liner and pad.

7. A device useful in forming anodic films on parts comprising a tubular dielectric member adapted to be grasped and manipulated by the operator, a metal liner in the member, a pad of absorbent material secured in the liner and extending from an end of the member so as to be engaged with the parts being treated, the liner being adapted to contain a supply of electrolyte for wetting the pad, a metal piston operable in the liner to force electrolyte therefrom into the pad, a rod on the piston for operating the same, and means connected with the rod for supplying electrical current to liner and pad.

' FRANK W. THOMAS.

ELI SIMON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 203,256 Frobisher May 7, 1878 737,882 Strecker Sept. 1, 1903 1,416,929 Bailey May 23, 1922 1,552,591 Batenburg Sept. 8, 1925. 1,805,215 Hammond May 12, 1931 1,908,222 Conlin May 9, 1933! 2,108,700 Adey Feb. 15, 1938 2,305,990 Prest .Dec. 22, 1942 2,408,910 Burnham Oct. 8, 1946 FOREIGN PATENTS Number Country Date 673,190 Germany Mar. 17, 1939 2,081 Sweden July 23, 1889 OTHER REFERENCES The Anodic Oxidation of Aluminum and its' Alloys as a Protection Against Corrosion, De-.

Transactions of the Electrochemical Society;

Vol. 88 (1946),PP. 325-331. 

1. THE METHOD OF FORMING A CORROSION RESISTANT ANODIC COATING ON THE SURFACE OF A METAL PART WHICH COMPRISES SUPPLYING A LIQUID ELECTROLYTE TO A POROUS PAD, CONNECTING SAID PART AND PAD WITH THE OPPOSITE SIDES OF AN ELECTRIC ENERGY SOURCE WHICH SUPPLIES A VOLTAGE OF FROM 20 TO 200 VOLTS AND CURRENT DENSITY OF FROM APPROXIMATELY 180 TO APPROXIMATELY 2750 AMPERES PER SQUARE FOOT, BRINGING THE SURFACE OF SAID PART AND THE PAD INTO ENGAGEMENT, AND MOVING THE PAD AND PART RELATIVE TO ONE ANOTHER WHILE SAID ENGAGEMENT IS MAINTAINED AND WHILE THE PART AND PAD ARE CONNECTED WITH SAID ENERGY SOURCE TO PROGRESSIVELY FORM A CORROSION RESISTANT ANODIC FILM ON SAID SURFACE. 